Liquid heating process



NvENToRS n.. ATTORNEYS H. HuEsLER ETAL.

LIQUID HEATING PROCESS Filed May 14, 1962 /Ql/O/ July 20, 1965 vwhere continuous operation is required. .known mechanical treatments possess the disadvantages 1of requiring constant attention.

Ilt is, therefore, among the objects of the present in- United States Patent The present invention relates to a non-encrustating heating process wherein the materials requiring thermal increase normally encrustate or foul heat exchanger surfaces as the temperature is increased. The present invention also relates to a process for the introduction of vapor at a lower pressure into a system at a higher .pressure and to the efficient utilization of the heat content `of that vapor. This application is a continuation-in-par-t of our copending application Serial 483,567 filed Janin ary 24, 1955, now abandoned.

Certain liquors when placed in normal heat exchange relationship with externally applied heat through a metallic heat exchange surface tend to solidify or polymerize 1 against -the walls of the exchanger. This tendency causes loss of exchanger efficiency and ultimate plugging or fouling of the exchanger. The liquors having such tendency are usually organic materials such as alkaline base pulping liquors (calcium lignin sulfonate), finely comminuted garbage, 4sewage and certain other organic .materials which tend to polymerize or solidify against the hot surfaces :of heat exchangers. Such resinous formations at the exchange surface tend to entrap inorganic materials and salts. The temperature at and immediately adjacent to the exchanger surface may be so hot that dimerization, trimerization and even polymerization of many of the organic materials occurs at the face of the normal metallic transfer barriers. Still, such substances in various chemical processes, such as vanillin extraction from calcium base sulphite pulping liquors must be heated to relatively high temperature beyond the temperature at which fouling of heat exchange surfaces occurs. Thus, when calcium base pulping liquor is heated above 220 degrees Fahrenheit the material (predominantly calcium lignin sulfonate) solidies against the heat exchanger surfaces.

Several known approaches have been utilized in attempts to avoid the fouling of heat exchanger difficulties with such materials. Several such approaches have gained commercial significance. In one, several exchangers are provided yand the ma-terial tending to solidify on the exchange surfaces is run through one of the exchangers until the eiiciency drops markedly; then the other exchangers are shunted in successively while the down exchanger is cleaned and flushed. This type of operation has mechanical distadvantages which are obvious. A second approach has been the use of increased flow velocities through the exchanger tubes to accomplish a sweeping effect which theoretically wipes.

the exchanger surfaces of any accumulation. Where, however, it is necessary to increase the temperature of the liquor tending to solidify beyond a few degrees, this system has practical limitations. The exchangers required are unduly elongated and if circuitous paths Iare i. introduced, where velocities are non-uniform, the tendency to accumulate irregular knots `of materials, is accentuated causing ultimate plugging. The necessity for high pressure fluid pumps also presents considerable disadvantage. Neither system presents a complete and satis- .f

factory `solution to chemical processing of such material Other less vention to teach a non-encrustating method for heating 3,i95,35 Patented July 20, 1965 ICC liquors to tempertaures in excess of that at which normal solidication `and encrustation is to be observed on the exchanger surfaces when conventional methods of heat exchange are employed.

It is among the objects of the present invention to teach a method for introducing steam at a lower pressure into a system at a higher pressure concurrently utilizing the heat content of that steam in a heating process.

The invention sought to Ibe patented resides in the concept of an encrustation-free process for heating a liquor, said liquor containing heat solidifiable or solubilized materials with a reverse order of solubility, to a desired temperature above that at which said materials encrustate heat exchanger surfaces, which includes the steps of: heating water in the presence of a non-condensible gas to form steam and introducing the resultant mixture of steam and non-condensible gas into the liquor to be heated, said liquor 'being at a pressure greater than the partial pressure of the said steam bu-t less than the total pressure of the said mixture of steam and non-condensible gas, until said liquor is heated to the aforesaid desired temperature.

yAs used herein, the term non-con-densible gas means a gas incapable of being condensed at the temperatures and pressures employed in the present process, i.e., a gas with a lower critic-al temperature such as oxygen -or nitrogen, yor a mixture of such gases such as air. The nature of the non-condensible gas employed is not critical to the heating yprocess of the present invention. There is no requirement tha-t the non-condensible gas employed be inert under the conditions of the heating process; it is ofter =desirable that the gas be reactive.

The manner and process of using this invention is illustrated -by the drawings and by the following general description and examples which set forth the -best mode contemplated by the applicants of carrying out the invention so as to enable any person skilled in the art of heat exchange t-o use the same:

In the drawing:

:FIGURE 1 is a schematic diagram showing the association of apparatus in accomplishing heating in accord with the present invention.

FIGURE 2 is a schematic diagram showing a modified association of apparatus wherein heating of the incoming gas-liquid material is accomplished by utilizing the eiuent material from the chambers shown as a heating medium.

FIGURE 3 is a schematic diagram showing a modification ofthe apparatus shown in FIG. 2 wherein only a part of the heating of the gas-liquid material is obtained from the effluent from the chambers and external heat iS added as shown. In phantom line is shown an inlet to the chambers for the introduction of reactants where desired.

When dealing with the heating of liquors containing materials whichtend to coat the walls of heat exchanger surfaces, it was found that if a liquid and a vnon-condensible gas were mixed and heated and the resulting vapor-gas mixture were introduced into the liquor to be heated, no fouling occurred. The heat for the elevad the equipment was observed .and no fouling of the equipment occurred.

Further, it was found that where kthere was an exothermic reaction between the admitted gas and the liquor being heated, the heat liberated from such reaction was frequently utilizable to elevate the temperature of the water and non-condensible gas mixture so as to render the process described self-sustaining. For example, such a selfsustaining process appeared where a raw alkaline liquor containing calcium lignin sulfonate was partially oxidized as in the preparation of vanillin. Ordinary heat exchange apparatus consistently fouled and required constant service to maintain continuity of production. Air and waterV were mixed, heated, and the resulting vapor introduced to the liquor. The liquor being at a relatively low temperature, (below 22() degrees Fahrenheit) substantially below that at which solidication normally occurs, it was satisfactorily uid in the process handling equipment. The hot vapors introduced caused substantial turbulence and caused an almost instantaneous elevation of the liquor temperature.

As mentioned above, the process of the present invention utilizes the heating of a liquor with vapor produced in the presence of a non-condensible gas. This is a particularly important aspect of the present invention because the liquor being heated is at superatrnospheric pressure. Where steam is produced without the system and not under the partial pressure of a non-condensible gas, getting the vapor into the system whichl contains the liquor to be heated under a pressure greater than that of the vapor has been accomplished in the prior art by either one of two methods. The iirst is to generate steam in a separate boiler at a pressure higher than the system into which it is to be introduced. Alternatively, lower pressure steam is compressed to a pressure higher than that of the system into which it is to be introduced and then introduced into that system. Both ofthese processes are costly and energy consuming procedures.

According to the present invention, water, a non-corn- Y The. water is f required lpressure for injection into the system.- The water can be heated and'converted to vapor by reactor eiiiuents, low pressure steam or other economical source of heat. Use of the non-condensible gas supplies the additional pressure necessary to introduce the lower pressure steam into the liquor to be heated at a higher pressure.y Energysavings result because the total pressure does not have to be steam.

SPECIFICy DESCRIPTION Referring with particularly first to FIGURE l, it will be seen that theV process and apparatus therefor, in its elemental form, requires only the simplest of process equipment. The liquor material, normally demonstrating tendencies to foul exchanger equipment during heat exchange, enters as diagrammatically shown and is easily pumped at relatively low temperatures by means of `a pump 11. The pump 11v delivers the liquor material in a suspended condition to the chamber 12.k Gas and liquid are'mixed and enter conduit 13 where the gas and liquid mixture is passed into the heater 14. A compressor (not shown) and pump (not shown) supply the respective gas and liquid to the system. The heater 14, heated from an external source, elevates the temperature of the gas and liquid mixture. The thus thermally enhanced mixture produced in the heater 14 are conducted through tubing 15 to the chamber 12 and are there introduced into the liquor material. During this intimate admixture of gas-liquid mixture and liquor material in the chamber 12 the temperature of the liquor is elevated beyond the temperature at which solidification of the material on exchanger walls was ordinarily observed. No fouling of the chamber 12 was d foundl and although the liquor material was passed through the tube 16 to the second chamber 17, no scaling, fouling, or solidication of material was observed in the equipment after continuous and prolonged operation. The drawings illustrate plural chamber installations but a single chamber having a suitable capacity can `be employed.

Subsequently, Where it was sought to oxidize some of the materials in the chambers 12' and17, the gas introduced was shifted tofan oxygen containing gas (air) and the exothermic oxidation reaction provided heat in excess of that required to heat the gas-water mixture utimately used as a heat media.

As shown in` FIGURE 2, the oxidized material was passed out ofthe chamber 17 and into countercurrent heat exchange relationship Vwith the incoming mixture of air and water in the modilied heater'14. Valves 1S and 19 were provided to suitably meter the tlowfof material supplying heat to the heater 14. Despite the heat exchanger surface then involved no fouling occurred during heat transfer and inspection. `of valve and valve seats showed no appreciable solidification orY polymerization of the llowing material. In other regards, the flow circuit of the apparatus in FIGURE 2 was substantially a duplicate of the equipment illustrated in FIGURE 1.

In this connection it is believed signicant to note that no exchange surfaces (transfer'barriers) ,are actually used for heating the iiowing liquor material.. The heating in chamber 12 and 12 is accomplished by mixing high level energy material with the relatively cool liquor material. Since no metallic heat exchanger surfaces are involved in the heating yof the liquor, no opportunityfis provided for localized heating at the exchange surfaces causing the usual fouling. The flow conditions and agitation attending the intimate heat exchange between the liquor material and the steamair mixture substantially avoids polymerization at any metal interphase. Flow through the system is continuous-and unimpeded by fouling usually attending the heating of such liquor material.

InFIGUREiB, an apparatus is clearly disclosed schematically to show another modification of the present invention where the heat residing in the reaction products in the chambers 12 and V17 is insuicient to supply all of the heat necessary to elevate the gas-liquid mixture to a suitable temperature for sustaining the reaction. In such an instance outside heating is required and the auxiliary heater 14a supplies heat from an external source to supplement the preheated gas-liquid mixture. As in FIGURE 2 the reaction products, yor at least a part of them, from chamber 17 pass to and through the heater 14 which serves as a preheater. In other particulars the circuit is identical with the process arrangementl as described in FIGURE 2. The apparatus described in'FIGURE 3 may also be considered to showa starter for an ultimately selfsustaining system of heating. Ifthe reaction products, as in FIGURE 2, are suicient in heat to render the system self-sustaining the auxiliary or starting heater 14a is unnecessary and may be shut off.

Also in FIGURE 3 and shown in phantom line is the modification of chamber 12 showing an entry l20 through which reactants separate from either the liquor or gasliquid mixture are introduced to the system if desired.

VThus a process has been described wherein a gas, such as air, is mixed with a liquid (such as water), heated, and the gas-liquid (vapor) mixture injected into a liquor material which normally solidifies against heat exchanger surfaces. The liquor material is elevated in temperature vwithout fouling the rconducting equipment and intimate heat exchange has occurred. Where the heated liquor material reacts in the mixing chamber and the reaction is exothermic in character, the liquor material may then be used to accomplish at least partial heating of the gaswater mixture. Even residual heat from purely endo thermic reactions are Vpotentially of assistance in minimizing external heat requirements, as shown in FIGURE 3.

A constant pressure is maintained in the system to permit desired thermal elevation.

The following example illustrates an instance where serious fouling occurred when water was mixed with raw alkaline liquor (calcium base) and the mixture heated to 295 degrees Fahrenheit in a metallic barrier and was then introduced into a chamber with desired quantities of air for vanillin production:

Example l Raw alkaline pulping liquor was pumped into a heat exchanger at a rate of 23.3 gallons per minute with 6.6 gallons per minute of water. The liquor was admitted to the exchanger at 140 degrees Fahrenheit with the water at about 60 degrees Fahrenheit. The liquor-water mixture was discharged from the heat exchanger at 295 degrees Fahrenheit. The heated mixture was then flowed Raw alkaline liquor was pumped into a chamber at about 140 degrees Fahrenheit at a rate of about 23.3 gallons per minute. Water at 60 degrees Fahrenheit, and fed at a rate of about 55.6 pounds per minute, was mixed with air at about 80 degrees Fahrenheit and at a rate of about 36.2 pounds per minute and both the water and air were heated to about 324 degrees Fahrenheit. The thus heated air-water mixture was led into the chamber as shown in FIGURE 1 and merged with the raw alkaline liquor. An intermediate temperature of approximately 263 degrees Fahrenheit resulted from the mixture of the hot and relatively cool materials admitted to the chamber. This arrangement was used continuously with the liquor under a pressure of about 154 pounds per square inch gauge. Subsequently the materials were led from the chamber and no fouling of any of the surfaces involved in conducting the materials wasy observed although the run was made continuous.

The following example demonstrates the operation of another run yin accord with the present invention with liquor at a pressure of about 2020 pounds per square inch gauge and demonstrates the self-sustaining character of the operation so as to render the heating independent of outside heat except by Way of starting. Any starting heat may be turned off in continuous operation and the apparatus arrangement in such an instance is comparable to the schematic diagram in FIGURES 2 or 3.

Example 3 With the pressure in the system maintained at 2020 pounds per square inch gauge and with water at about 60 degrees Fahrenheit at a iiow rate of about 116 pounds per hour and mixed with air entering at about 140 degrees Fahrenheit and at a rate of about 142 pounds per hour, the mixture was heated to a temperature of 503 degrees Fahrenheit. A heat balance at this point indicated:

B.t.u. per hour Steam 72,300 Water 27,700 Air 16,600

Total heat in air-water mixture 116,600

This air-water mixture was mixed with the stream of raw alkaline liquor (containing calcium lignin sulphonate) entering the chamber at degrees Fahrenheit and at a ow rate of about 451 pounds per hour. The heat content of the liquor material was about 52,000 B.t.u. per hour. After mixture in the chamber an intermediate temperature developed at about 325 degrees Fahrenheit. Considered at this point, the desired temperature, above that at which fouling was to be expected, had been achieved ignoring any reaction occurring within the chamber.

However, the material in the chamber was reacted with the incoming oxygen contained in the air mixture and the exiting material from the reaction was observed to be -in the neighborhood of 570 degrees Fahrenheit. This provided ample heat to accompli-sh the desired heating of the air-water mixture in the heater. Continuous operation as indicated in FIGURE 2 proceeded with no fouling of the apparatus walls.

Similar runs, demonstrating the effectiveness of the presently described process on both sewage and garbage in water, were made. As heated in accord with Example 1 (conventional exchange) many of the constituents of the materials showed soliditication or polymerization at about 2004230 degrees Fahrenheit. Above these temperatures, increased deposition on the equipment occurred.

As will be seen from the Example 2, and ignoring any exothermic reaction, the liquor-gas-liquid material in chamber 12 was at least above the temperature at which calcium lignin sulfonate normally commenced to encrustate usual exchanger surfaces, and at the intermediate temperature of 295 degrees Fahrenheit the material leaving chamber 17 could substantially preheat the incoming air-water mixture to substantially reduce the ouside heat `required toV supply an air-water mixture to the chamber 12 at 324 degrees Fahrenheit. By using the modication illustrated in FIGURE 2 such a saving of heat is accomplished.

Similarly, where endothermic reactions occur, the ex- ,cess of heat available after reaction is still available for conventional exchange against the incoming gas-liquid mixture for preheat and attendant heat saving.

When the process herein described was adapted, as in Examples 2 and 3, to sewage and garbage in water similar results were obtained. No fouling was observed and chamber exhaust temperatures attending exothermie reaction within the chamber demonstrated the process as shown in FIGURE 2 and Example 3, wherein the outside heat was unnecessary in the heater and the required temperature of gas and water was obtained using the heat available in the chamber materials cycled against the incoming mixture of water and air.

The process of the present invention avoids compressing and pumping steam into the system but rather only requires the pumping of water (a non-compressible liquid) together with a non-condensible gas into the system. Heat is then applied to this mixture of water and non-condensible gas to form steam Within the system and the resultant steam-non-condensible gas mixture is readily introduced into the liquor to be heated where the steam gives up Iits heat of condensation. This procedure avoids the making and using of high pressure steam.

In Example 3, the liquor in the reactor is at 160 degrees Fahrenheit and at a pressure of 2020 pounds per square inch gauge. To bring this liquor to the desired temperature of 325 degrees Fahrenheit requires a mixture of air and steam at a temperature -of 503 degrees Fahrenheit. The part-ial pressure of steam in the mixture is about 700 pounds per square inch gauge. Were it not for the presence of the air, steam at least 638 degrees Fahrenheit and at 2020 pounds per square inch gauge would have been required. The net result is that the liquor has been heated to the desired temperature with 700 pounds per square inch gauge steam instead of 2020 pounds per square inch gauge steam.

Similarly in Example 2, it was desired to heat the i grees Fahrenheit and at 185 pounds per square inch gauge would have had to be used.

A convenient continuous heating process has been described for materials not amenable to ordinary heatingwithout fouling the heating apparatus and a self-sustaining heating system is made available where the process looks to an associated reaction which is exothermal in character. Various modifications of this invention will suggest themselves to those skilled in the art and the invention is not to be limited to the above-offered examples. The subject matter which the applicants regard Vas their invention is particularly pointed out and distinctly claimed as follows:

1. A process for directly heating to a selected temperature at superatmospheric pressure a liquor containing heat solidiiiable materials or solubilized materials having a reverse order of solubility which encrustateheat exchange surfaces when the liquor is indirectly heated, which comprises intimately mixing in concurrent ilow relationship the liquor at a temperature below its encrustation temperature and at the selected superatmospheric pressure withk a gaseous mixture of liquid yvapors and a noncondensable gas at a temperature above the selected temperature and at a pressure greater than the pressure of the liquor such that the partial pressure of the` liquid vapors in the mixture is less than the pressure of the liquor in a proportion of liquor to liquid vapors-noncondensable gas mixture which heats the liquor to the selected temperature.

2. The process according to claim l wherein the liquid vapors are steam.

3. A process for directly heating to a selected temperature at superatmospheric pressure an aqueous liquor containing heat solidifiable materials or solubilized materials having a reverse `order of solubility which encrustate heat exchange surfaces when the aqueous liquor is indirectly heated, which comprises intimately mixing `in concurrent flow relationship the aqueous liquor at a temperature below its encrustation temperature and atthe selected superatmospheric pressure with a gaseous mixture of steam and air at a temperature above the selected temperature and at a pressure greater than the pressure of the liquor such that the partial pressure of the steam in the mixture is less than the `pressure of the liquor in a proportion `of liquor to steam-air mixture which heats the liquor to the selected temperature.

4. A process according Vto claim 3 whereinvthe steam and air mixture is at least partially heatedby indirect heat exchange with the heated liquor. Y

5. A process according to claim 3 wherein the liquor is oxidizaole by the air-steam mixture at V.the selected temperature.

6. .A continuous process foroxidizing an aqueous liquor, oxidizable at elevated temperatures and superatmospheric pressures inthe aqueous liquid phase, containing heat solidiiiable materials or solubilized materials having a reverse order of solubility which encrustate heat exchange surfaces when `the liquor is indirectly heated to an oxidizing temperature, which comprises the steps :of

(a) continuously pumping the aqueous liquor at a temperature below its encrustating temperature to a mixing zone at a selected pressure sufficient to permit the liquor to be-heated to an oxidizing temperature therefor,

(b) continuously heating a mixture of water and air to a temperature above the oxidizing temperature of the liquor to provide a heated mixture of air and steam at a total pressure above the selectedk pressure in which lthe steam has a partial pressure less than the selected pressure,

(c) continuously mixing the heated air-steam mixture with the aqueous liquor in the mixing zone as a concurrently owing intimate mixture in a proportion which heats the aqueous liquor lto a temperature which oxidizes ythe liquors,

(d) continuously passing the `oxidized liquor in indirect counter-current heat exchange `'relationship with the incoming air-Water mixture to produce the air-steam mixture.

7. A process according to claim 6 wherein the proportion yof air t0 water on a weight basis is at least 0.65 to 1 and the mixture thereof is heated to at least 324 F.

References Cited by the Examiner UNITED STATES lPATENTS n 2,169,683 8/39 Dunham et al 60-39.56 2,759,328 8/56 Cockrell 210-56 X FOREIGN PATENTS 5,844 of 1890 Great Britain.

OTHER REFERENCES Water Treatment for lndustrialand Other-Uses, Nordell, 1951, Reinhold, VNew York, pp. 189-193.

' MORRIS O. WOLK, Primary Examiner. 

1. A PROCESS FOR DIRECTLY HEATING TO A SELECTED TEMPERATURE A SUPERATMOSPHERIC PRESSURE A LIQUOR CONTAINING HEAT SOLIDIFIABLE MATERIALS OR SOLUBILIZED MATERIALS HAVING A REVERSE ORDER OF SOLUBILITY WHICH ENCRUSTATE HEAT EXCHANGE SURFACES WHEN THE LIQUOR IS INDIRECTLY HEATED, WHICH COMPRISES INTIMATELY MIXING IN CONCURRENT FLOW RELATIONSHIP THE LIQUOR AT A TEMPERATURE BELOW ITS ENCRUSTATION TEMPERATURE AND AT THE SELECTED SUPERATMOSPHERIC PRESSURE WITH A GASEOUS MIXTURE OF LIQUID VAPORS AND A NONCONDENSABLE GAS AT A TEMPERATURE ABOVE THE SELECTED TEMPERATURE AND AT A PRESSURE GREATER THAN THE PRESSURE OF THE LIQUOR SUCH THAT THE PARTIAL PRESSURE OF THE LIQUID VAPORS IN THE MIXTURE IS LESS THAN THE PRESSURE OF THE LIQUOR IN A PROPORTION OF LIQUOR TO LIQUID VAPORS-NON-CONDENSABLE GAS MIXTURE WHICH HEATS THE LIQUOR TO THE SELECTED TEMPERATURE. 